The present invention is directed to spraying apparatus which includes a fluid storage tank having an agitator for mixing the fluid in the fluid storage tank and an anti-vortex device for preventing the formation of a gyrating vortex in the fluid as the fluid is discharged from the fluid storage tank.
Emulsifiable or wettable powders are frequently employed as active ingredients for a variety of applications, including agricultural herbicides, insecticides or fungicides, as well as other industrial uses. When these emulsifiable or wettable powders are mixed in water solutions or mixed with liquid fertilizer, the solid particles tend to settle and collect at the bottom of the fluid storage tank since these particles are normally only held in suspension rather than being dissolved in the solution. In order to improve the performance of spraying apparatus for spraying fluids containing these emulsifiable or wettable powders, it is necessary to agitate the fluid in the fluid storage tank in order to maintain these emulsifiable or wettable powders in substantially homogeneous suspension at all times.
As is generally known in the art, spraying apparatus of this type generally includes a fluid storage tank which is connected to a pump for pumping the fluid stored in the fluid storage tank to spray heads or nozzles. Normally, agitation of the fluid in the fluid storage tank is accomplished by returning a portion of the solution from the pump back to the fluid storage tank viz a bypass pipe. The momentum of the fluid in the bypass pipe agitates the fluid in the fluid storage tank. An example of such a spraying apparatus is shown in U.S. Pat. No. 2,692,798 issued to Hicks on Oct. 26, 1954. In this patent, the bypass pipe protrudes into the fluid storage tank and a biased agitator cap is responsive to the pressure of the fluid in the bypass pipe to permit the bypass fluid to flow into the fluid storage tank to thereby mix the fluid contained therein.
Different arrangements have been used in the prior art to improve the agitation in such spraying apparatus. For example, Venturi mixer nozzles have been connected on the end of the bypass pipe near the bottom of the fluid storage tank to draw the settling or precipitating particles and the surrounding liquid into the Venturi mixer nozzle whereupon it is discharged with force sufficient to agitate the fluid in the fluid storage tank. Agitator devices which employ Venturi mixer nozzles are shown in U.S. Pat. No. 3,826,474 issued to Pareja on July 30, 1974 and French Pat. No. 1,142,557 published on Sept. 19, 1957. Other types of nozzles have been employed in the prior art for improving the agitation of the fluid in the fluid storage tank. In U.S. Pat. No. 3,661,364 issued to Lage on May 9, 1972, a pressure nozzle is located near the bottom of the fluid storage tank in order to subject the fluid in the fluid storage tank to a rotationally symmetrical circulatory movement as the fluid in the bypass pipe impinges against the bottom of the tank. As a result of the impact of the fluid from the bypass pipe on the tank bottom, a particular mixing effect is achieved.
Another technique employed in the prior art for mixing the fluid in a fluid storage tank is a sparging system in which agitation of the fluid is achieved by introducing compressed air into the fluid. For example, in U.S. Pat. No. 2,224,741 issued to Metrick et al on Dec. 10, 1940, compressed air is forced from an inlet pipe through spiral channels near the bottom of the fluid storage tank to thereby mix the fluid in a spiral rotating fashion. Similarly, U.S. Pat. No. 3,276,698 issued to Wood on Oct. 4, 1966 shows a system in which compressed air is introduced into the fluid through a protruding pipe having a movable closure cap responsive to the pressure of the compressed air. The closure cap overlays the opening of the protruding pipe when no air is fed to the agitator. Under air pressure, the closure cap rises to create an annular opening through which the compressed air passes into the fluid in the fluid storage tank. The underside of the closure cap includes a plurality of spiral ribs which impart a spiral rotating motion to the compressed air as it passes through the annular opening.
While the above systems have been generally acceptable and widely used in the past, these systems fail to provide adequate control of the mixing process and they often result in localized agitation. These systems either fail to mix enough of the fluid or they overmix. By undermixing, the solid particles that are not in solution tend to fall out as sediment and are no longer fed to the spray heads or nozzles through the pump. On the other hand, overmixing can cause certain combinations of herbicides, fungicides, insecticides, and fertilizers to form a gel-like consistency. Therefore, there is need for a device which overcomes these disadvantages by providing more precise control of the mixing of the fluid in the fluid storage tank.
In addition to the disadvantages of prior art agitators, the pump in prior art spraying apparatus has a tendency to cavitate or suck in air as the fluid is withdrawn from the fluid storage tank. In particular, when the fluid outlet pipe is connected to the bottom of the fluid storage tank, it is quite common for a gyrating vortex to be generated in the fluid as it enters the fluid outlet pipe. Cavitation of the pump is caused by creating excessive low pressure at the suction side of the pump which either vaporizes the fluid or causes such a quantity of the fluid to move into the pump that a gyrating vortex is generated within the fluid. This gyrating vortex or hollow core permits air to enter the pump and causes the pump to lose prime and invariably causes a loss of pump efficiency. As a result, rapid wear on the pump impeller occurs.